1. Field of the Invention
The present invention relates to an ink set, an ink-jet recording method, a recording unit, an ink-jet recording apparatus and a method for reducing the bleeding in a multi-color image where different-color regions abut each other.
2. Related Background Art
The ink-jet recording method, capable of high speed printing and multi-color printing with less noise, carries out recording by ejecting an ink droplet to attach it to the recording medium such as paper, where the ink droplet is generated by various processes such as the electrostatic suction process by applying a high voltage, the process using a piezoelectric element to give a mechanical vibration or displacement to ink and the process heating ink to form a bubble to use its pressure (so-called bubble jet process).
When a color image is formed on a recording medium such as plain paper or bond paper, however, the above conventional ink-jet recording method often cannot provide a satisfying image because of a phenomenon called bleeding (color blurring or uneven ink mixing at the boundary of different color images) as a result of applying color inks one after another before ink fixation.
As means for solving such problems, Japanese Patent Application Laid-Open No. 55-65269 describes the use of an ink added with a compound for enhancing the penetrability such as a surfactant, and Japanese Patent Application Laid-Open No. 06-57192 describes an ink-jet recording ink set capable of preventing bleeding, which is comprised of a black ink containing at least one anionic dye and a yellow ink containing at least one cationic dye and a polyvalent precipitant.
However, when a penetrability-enhancing compound such as a surfactant is added to the ink as disclosed in Japanese Patent Application Laid-Open No. 55-65269, ink penetration is enhanced and bleeding is suppressed to a certain extent, but there arises a problem such that the ink penetrates deep into the recording medium along with the coloring agent so that the image density becomes low. Besides, since the wettability to the surface of a recording medium is increased, the ink tends to spread on the surface sometimes resulting in low resolution and low printing grade. With the ink-jet ink set described in above Japanese Patent Application Laid-Open No.6-57192, in which the black ink contains at least one anionic dye as a coloring agent and the yellow ink contains at least one cationic dye and a polyvalent precipitant, bleeding between black ink and yellow ink is suppressed to a considerable extent but bleeding between cyan ink and magenta ink, cyan ink and black ink, and magenta ink and black ink is not solved.
It is an object of the present invention to solve the above problems in the conventional art and to provide an ink set of three colors or more, capable of reducing the bleeding in a color image, forming a clear color image and improving the printing grade on a recording medium, as well as to provide an ink-jet recording method and ink-jet recording apparatus using the ink set.
According to one aspect of the present invention, there is provided an ink set for ink-jet recording of a color image on a recording medium by using three color inks, comprising:
(1) a first ink comprising a monohydric alcohol and an anionic dye which aggregates on contact with a polyvalent metal salt;
(2) a second ink comprising a polyvalent metal salt and an anionic dye which does not aggregate on contact with the polyvalent metal salt; and
(3) a third ink comprising a cationic dye, or a pigment and a dispersant.
According to another aspect of the invention, there is provided an ink set for ink-jet recording of a color image on a recording medium by using four color inks or more, comprising:
(1) a first ink comprising a self-dispersible carbon black with a cationic hydrophilic group directly or through another atomic group bonded to the surface thereof;
(2) a second ink comprising a monohydric alcohol and an anionic dye which aggregates when the second ink contacts with a liquid containing a polyvalent metal ion;
(3) a third ink comprising a polyvalent metal ion and an anionic dye which does not aggregate even when coexisting with the polyvalent metal ion; and
(4) a fourth ink comprising a pigment and an anionic dispersant for dispersing the pigment in the liquid.
According to a further aspect of the invention, there is provided an ink set for an ink-jet recording of a color image on a recording medium by using four color inks or more, comprising:
(1) a first ink comprising a self-dispersible carbon black with a cationic hydrophilic group bonded to the surface thereof directly or through another atomic group;
(2) a second ink comprising an anionic dye which aggregates when the second ink contacts with a liquid containing a polyvalent metal ion;
(3) a third ink comprising a polyvalent metal salt and an anionic dye which does not aggregate even when coexisting with a polyvalent metal ion; and
(4) a fourth ink comprising a cationic dye and a monohydric alcohol.
According to a still further aspect of the invention, there is provided an ink-jet recording method for forming a multi-color image comprising a step of:
ejecting respective three color inks by an ink-jet process, wherein the three inks correspond to the first ink, the second ink and the third ink constituting the above three color ink set.
According to a still further aspect of the invention, there is provided an ink-jet recording method for forming a multi-color image comprising a step of:
ejecting respective four color inks by an ink-jet process, wherein the four inks correspond to the first ink, the second ink, the third ink and the fourth ink constituting one of the above four color ink sets.
According to a still further aspect of the invention, there is provided a recording unit comprising: a first ink container, a second ink container and a third ink container respectively containing the first ink, the second ink and the third ink constituting an ink set and an ink-jet head for ejecting the ink contained in each ink container.
According to a still further aspect of the invention, there is provided a recording unit comprising: a first ink container, a second ink container, a third ink container and a fourth ink container containing the first ink, the second ink, the third ink and the fourth ink constituting one of the above four color ink sets and an ink-jet head for ejecting the ink contained in each ink container.
According to a still further aspect of the invention, there is provided an ink-jet recording apparatus comprising: a first ink container, a second ink container and a third ink container respectively containing the first inks the second ink and the third ink constituting the above three color ink set, and an ink-jet head for ejecting the ink contained in each ink container.
According to a still further aspect of the invention, there is provided an ink-jet recording apparatus comprising: a first ink container, a second ink container, a third ink container and a fourth ink container respectively containing the first ink, the second ink, the third ink and the fourth ink constituting one of the above four color ink sets and an ink-jet head for ejecting the ink contained in each ink container.
According to a still further aspect of the invention, there is provided a method for alleviating bleeding in a multi-color image where different color regions are adjacent to each other, wherein the images formed with at least two color inks among three color inks respectively corresponding to the first ink, the second ink and the third ink constituting the above three color ink set.
According to a still further aspect of the invention, there is provided a method for alleviating bleeding in a multi-color image where different color regions are adjacent to each other, wherein the images are formed with at least two of four color inks respectively corresponding to the first ink, the second ink, the third ink and the fourth ink constituting one of the above four color ink sets.